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jmc

number theory junior

Problem

Terri produces a sequence of positive integers by following three rules. She starts with a positive integer, then applies the appropriate rule to the result, and continues in this fashion. Rule 1: If the integer is less than 10, multiply it by 9. Rule 2: If the integer is even and greater than 9, divide it by 2. Rule 3: If the integer is odd and greater than 9, subtract 5 from it. A sample sequence: Find the term of the sequence that begins
(A)
(B)
(C)
(D)
Solution
We could start by looking for a pattern. From here, we see that we have a pattern of after Our problem is now really Find the term of the sequence that goes There are 5 terms in each repetition of the pattern, and , so the answer is
Final answer
D